The semiconductor industry is continually innovating in fabrication processes. This innovation has resulted, and will likely continue to result, in the development of new structures and, as such, new semiconductor devices. More specifically, this innovation has taken semiconductor fabrication from (a) having active circuitry in largely flat layers disposed substantially at or in the very top of a single semiconductor substrate, toward (b) providing active circuitry at one or more of various layers, in new substrates, or in combination(s) of substrates, including between two or more bonded or stacked substrates. This innovation has resulted in semiconductor devices such as Micro Electro Mechanical Systems (MEMS), Micro Electro Optical Mechanical Systems (MOEMS), Silicon on Insulator (SOI) devices and Light Emitting Diodes (LEDs).
Fabrication innovations in the semiconductor industry generally are accompanied by innovations in test and quality control. In test and quality control, tools and processes are employed that identify defects in particular chips/wafers, while also generally contributing to improvements in fabrication (e.g., process control so as to increase yield) and reliability (e.g., to anticipate and help control failure parameters of products in the field). Such tools and processes are directed, among other things, to imaging and inspecting semiconductor devices, particularly as to the semiconductor structures thereof. Accordingly, when fabrication innovation results in new semiconductor structures, innovations generally keep pace in tools and processes so as to enable imaging and inspection of such structures.
As would be expected for conventional semiconductor devices having active circuitry substantially at or near the surface of a single semiconductor substrate, conventional imaging and inspection tools and processes are employed. These tools and processes enable identification of features located substantially at or near the wafer's surface, e.g., within approximately 200 Angstroms of the wafer's surface. Clearly, these tools and processes have capabilities paired to the structures that are to be imaged or inspected.
As for conventional semiconductor devices, new semiconductor devices generally need tools and processes that enable imaging and inspection of device's structure(s)'s relevant features, including to identify various conditions and to detect defects. However, these relevant features may be disposed other than at or near the surface of the substrate. Indeed, these relevant features within bonded or stacked substrates tend to be located inside the bonded or stacked layers (e.g., in the interface layer(s), including the characteristics of the bond itself). As such, for these and other new semiconductor devices, conventional imaging and inspection tends generally to be insufficiently effective, or even ineffective, if performed using the above-described conventional tools and processes.
Tools and processes have been developed that enable imaging and inspection of features relevant to the structure(s) of the above described semiconductor devices. To illustrate, tools and processes exist for imaging and inspection of semiconductor devices having bonded or stacked substrates, or other structures based on bonding or stacking materials. These tools and processes include infrared microscopy using high magnification optics under infrared light provided by bulbs; X-Ray imaging; and ultrasonic imaging.
Of these, ultrasonic imaging may be the most prevalent. It entails placing a wafer in a liquid bath, applying an ultrasonic signal and, using ultrasound wave flight measurement, constructing a map of the wafer bond's integrity. Even though prevalent, ultrasonic imaging has several drawbacks. These drawbacks include, as examples: the liquid bath tends to be detrimental to electronic production environments; it not only adds the steps described above, but also introduces additional steps before fabrication can proceed (e.g., to clean and dry the wafer); and it enables only the inspection for wafer bond defects, such that other relevant conditions or defects are identified/detected using additional imaging/inspection tools and/or processes.
The drawbacks of ultrasonic imaging are not present in infrared microscopy. Infrared microscopy, as illustrated in FIG. 1, typically entails using a halogen or other bulb light source 10 in conjunction with an appropriate infrared high-pass or band-pass filter 20 so as to generate infrared light. The infrared light is provided to irradiate objects 50 via a fiber optic light guide 2 and a lens system 3. In this configuration, the infrared light is directed to objects 50 via an internal beam splitter in the lens system 3. The infrared light, so directed, generally is reflected by objects 50 at various intensities (e.g., depending on the bond characteristics and other structural features of the semiconductor device) back up through the lens system 3 to an infrared camera 60 for image capture. Via such image, test and quality control may be performed, e.g., to inspect the relevant features, including to identify various conditions and to detect defects, such as in bonding and adjacent layer(s).
While infrared microscopy provides for imaging and inspection of semiconductor devices having bonded or stacked substrates, microscopy also tends to have drawbacks. As an example, a typical light source is a halogen or other bulb, which provides light across a broad spectrum, including infrared. In order to provide infrared light, then, an appropriate filter is used. As another example, a typical infrared camera in conventional microscopy arrangements is or employs, e.g., a vidicon camera, gallium arsenide detectors, microbolometers, or other scientific, professional or industrial-grade technologies which technologies tend to be technically more complex to develop, manufacture and use, while also tending to be produced in lower volumes and at higher costs than mainstream solid state imaging devices (e.g., standard, consumer-grade, silicon-based charge coupled devices or CMOS image sensors, used in, for example, consumer digital still cameras that are widely sold to average consumers in retail outlets).
Accordingly, it is desirable to have tools and processes that broadly enable imaging and inspection of the various features relevant to selected structure(s) of semiconductor devices. In addition, it is desirable to have tools and processes that enable imaging and inspection of features relevant to selected structure(s) of semiconductor devices, particularly where such structures and associated features are disposed other than at or near the surface of the device.